Telephony



H. S. TURNER.

TELEPHONY.

- APPLICATION mp0 020.4. 1915. 1,434,975,

Patented Nov. 7, 1922,

4 suns-sum 1. 4

n as E 2 H. S. TURNER.

TELEPHONY.

. APPLICATION FILED DEC- 4, l9l5. 1,434,975. Patented Nov. 7, 1922.

v 4 SHEEIS-SHEE] 2. ig-- H. S. TURNER. TELEPHONY.

' APPLICATIONJILED mac. 4. 1915. 1&34375 v Patented Nov. 7, 1922.

4 SHEEIS-SHEE] a. F1 .4.

H. .S. TURNER.

TELEPHONY. APPLICATION FILED 0c. 4.191s.

Patented Nov. 7 1922.

4 SHEHS-SHEE] 4.

Patented Nov. 7, i922.

HUBERT S. TURNER, OF WASHINGTON, DISTRICT OF COLUZMBIA.

TELEPHONY.

Application filed December To all whom it may concern.

Be it known that I, Hnnnnr S. TURNER, citizen of the United States, residing at Washington, in the District of Columbia, have invented certain new and useful Tmprovements in Telephony, of which the following is a specification.

The present invention has for one of its principal objects the provision of means whereby the simplicity and advantages ob tained by the use of an old and well known form of link connector or cord circuit together with the improvedservice obtained by using link connectors comprising features such as automatic disconnect, automatic recall, automatic ringing, automatic listening and secret service, etc., are combined in a new link connector circuit which is the subject of the present invention, in which the disadvantages inherent in both the cited link connector circuits are eliminated. The link connector circuit of this invention is adaptable for use with any of the well known forms of central oflice apparatus. I have chosen for illustrating the same a well known type of such apparatus and a well known type of link connector to which types. however, the invention is not to be restricted as it will be clear that the new features described may be adapted for use with other well known forms of apparatus and for use with other well known forms of link connector circuits, without departing from the principles involved.

In my invention, I add but one, two, three or four simple relays of a well known type to each link connector and by providing audible signal means for the operator, am enabled to approximate the advantages obtained by the use of the more complicated link connector comprising the automatic teatures mentioned,

In my invention when a calling or called ,party replaces=the substation receiver on its switch-hook, an audible signal is in stantaneously sounded in the connecting operators head receiver, unless the opera tor is actually engaged in answering a call or a recall or completing a connection. At the same time a busy test made on any multiple jack connected to the same line will give a signal distinctive to the disconnect condition of the line. Therefore, should another operator hear this disconnect busy signal on testing a line, the line need not be reported busy to the calling party but 4, 1915. Serial No. 64,967.

the operator could wait a moment until the connecting operator had time to remove the plug from the line jack. As the connecting operator can only need a moment or so to remove this plug after hearing the audible disconnect signal, the other operator would lose less time by waiting than if the line is report-ed busy and the calling party later on initiates a new call for the same line. A recall is made whenever a substation receiver is removed before the connection is taken down by the operator. Therefore. to obtain an instantaneous recall, a. subscriber need only depress the switch-hook once, instead of continuously moving it up and downas is the old practice. On making a recall, an audible signal distinct from the disconnect signal is instantaneously sounded in the connecting operators receiver, unless a call is being attended to. At the same time the line will test busy, thereby evading a connection being made to it by another operator. The operator can select the line making the recall as the supervisory lamp individual thereto is illuminated in a different manner than it is when a disconnect is signaled. The operator can listen in when a recall is made by either the calling or called party or both, but cannot listen in before a recall is made, thereby obtaining the secret service feature with the added advantage of being able to supervise the connection whenever it is necessary. lVhen the called line is manually or automatically rung the supervisory signal in- .dividual to the called line is ill uninated in a different manner than it is when the called party has answered, has replaced the receiver on its switch-hook or is signaling a recall, and if the calling party signals a disconnect or recall previous to the response of the called party, then the called line supervisory signal is displayed in the disconnect manner and the ringing current is cut off if automatic ringing is used. or if manual ringing is used, and operator cannot make the common mistake and continue to ring a called line when the calling party has already abandoned the call. When acall is initiated at a substation an audible line pilot signal is sounded in the operators receiver which may eliminate the disconnect signal or the disconnect and recall signals. or one or both of the latter may eliminate the pilot signal and sound it instead in the receiver of another operator who has means for answering the call. Means are provided whereby the recall signals may eliminate .the disconnect signals and if the latter take precedence over the linepilot signals it will be seen that precedence in calls will be given: first, to recalls; second, to disconnects; third, to new calls. Arrangements are made whereby the recalls may always take precedence over the disconnects and new calls, but the disconnects will only take precedence over the new calls when there is another operator available to attend to the new calls. Means are provided whereby when a line has two or more visual line signals mounted on different operators positions, one operator only will receive the audible line pilot signal, the same being transferred to one of the other positions when the first mentioned operator is busy, thereby avoiding the confusion of having two or more operators connecting to the same calling line at the same time. The audible signal system as described herein is a very elastic one and is capable of many variations, some of which I have shown and will hereinafter describe. However, I do not wish to be limited to the specific forms shown herein, as it will be readily understood as the description is proceeded with that by adding or subtracting from the number of the simple three contact relays used or by changing the connections thereof, that an infinite number of variations in the signal operating means may be obtained. Other objects than those hereinbefore mentioned will be apparent from the specification.

In the following description, reference will be had to my U. S. Patent No. 1,128,262 and my co-pending applications, Serial Nos. 11,06 and 45,232, new Patent No. 1,421,86 l, granted July 4:, 1922, as the present invention in respect to the automatic ringing and audible signals consists in improvements on the methods described therein.

In order to more fully describe my invention, reference will now be had. to the accompanying drawings forming a part of this specification, and wherein;

Figure 1 is a diagram illustrating how by adding one simple relay to each cord circuit and one to the operators equipment, the aforementioned well known type of link connector may be converted so that the audible line pilot signals, ringing supervisory signal and automatic ringing features may be used as hereinbefore mentioned; Figure 2 a diagram illustrated how by adding two simple relays of the same type as the well known supervisory relays, the same link connector may be converted so that the recall and disconnect audible signals and the recall and ringing visual signals are produced, the ad lition of eight relays of the supervisory type to the operators equipment providing the means whereby therecall audible signal takes precedence over a line pilot signal and the disconnect, the line pilot signal also taking precedence over the disconnect, the same relays performnig various line pilot audible signal transferring operations between adjacent positions so as to insure adequate team-work between operators; Figure 3 a diagram illustrating how by adding three simple relays of a well known type to the same link connector the automatic listening and ringing features are added to those shown in Figure 2, the addition of eleven relays of the supervisory type to tl e operators equipment providing the means for still further improvement in the teanr work between operators, and means whereby the disconnect audible signal causes the elimination of the line pilot signal pro vided, however, there is another operator who is able to attend to the calling line; Figure 4: a diagram illustrating a modification of the link connector illustrated in Fig ure 2 and a further division of the recall and disconnect features, wherein the calling and called parties have independent control over the recall signal; Figure 5 a diagram illustrating a modification of the link connector illustrated in Figure 3 with the same division of the recall and disconnect features; Figure 6, a diagram illustrating modification of the audible signal system illustrated in Figure 2, in which two groups of line signals are provided at each operators position, the pilot signals being independeiitly transferred; Figures";- and 8 diagrams illustrating modifications of the automatic listening means illustrated in Figures 3 and 5, and Figure 9 a diagram illustrating the means whereby when there are two or more visual line signals located at separate answering positions one operator only will receive the audible pilot signal and the other operator will receive the same only when the first mentioned operator is busy,

means being provided. for teamwork by the operators adjacent to both of the aforementioned operators.

In all the figures the talking circuit is shown by a heavy line, as well as the principal traced circuit for the transferred audible signals. v

Referring first to Figure 1, 1 and 2 represent telephone substations of a well known form. The removal of the telephone receiver at substation 1 closes a path for direct current through limbs 3l, thereby causing the energization of line relay 5. This gives path for current from battery 6 through elements 7, S, 9, 10 and ground, energizing pilot relay 7. This gives another path for current from battery 6 through elements 11, 12, 13, 1%, left winding of relay 15, 16, 17. 18 and grounchenergizing audible signal relay 15. However as soon as contacts iii-14 are separated this path is interrupted and relay 15 tie-energized.

. When contacts 131i are engaged again relay15 is once more energized whereupon the path is again interrupted. Therefore, a vibratory action of contact 13 is obtained and a pulsating current traverses primary 18 which induces an alternating current in secondary 19. As operators receiver :20 is connected to the two ternii nals of secondary 19 the alternating current produces an audible signal in the receiver. Hearing this signal the operator knows a line is calling and on looking over the visual line signals assigned to the position observes that line lamp 8 is energized, such energization having taken place when the aforementioned path was closed through relay 7. which relay is the pilot relay usually used in conjunction with a group of line sig nals at an operators position. The operatorv thereupon inserts answering plug 21 in answering jack22 which in a well known manner causes the energization of cut-off relay 23 and the consequent de-energization of line relay 5 and line lamp or signal 8. As the path through pilot relay 7 is thereupon opened the disengagement of contacts 1112 opens the path through relay 15, thereby stopping the production of the audible pilot signal.

The link connector illustrated in its general features is a well known one and need not be specifically described herein except in its bearing on the new features involved. The insertion of' plug 21 in jack 22 also connects limbs 3lto repeating coil windings 25-26 and when the operator manipulates listening key 27, in the well known manner, opera-tors receiver 20, secondary 28 and condenser 29 are connected to repeating coil windings 3l. The only changes made in this well known manner of connecting the operators telephone set to the repeating coil is that condenser 29 is shunted by the right winding ofrela-y15 and that repeating coil Winding 30 isc'onnected to spring 32- of key 27 by way of contacts 33--34 of relay Therefore. wl'ienever a key 27 is manipulated path is given for current from battery 6 through elements 30 34E, 86, right winding of relay 15, 28, 19 and 20 in multiple, 37,88,31 and ground energizing relay 15. The consequent attraction of the armature of relay 15 causes contacts 1314 to be disengaged, thereby preventing the sounding of the described audible signal .by the energization of another line lamp as long as a. key 27 remains manipulated. Therefore. while an operator is engaged in completing a connection or talking to a substation,- there is no interference caused by the sounding of the audible signal should another line signal be energized. The right winding of relay 15 is preferably of an extremely high resistance, so that but a small amount of direct current passes through receiver 20, thereby avoiding the disagreeable click produced in the receiver when an appreciable amount of current passes through the same. As a path for the voice currents is furnished around this winding by condenser 29, talking eiliciency is not diminished. As secondary 19 is in multiple relation to receiver 20. it may be of ahigh resistance, so as not to shunt an appreciable amount of the voice currents. Manually operated switch 16 may or may not be used. It is provided when it is desired to furnish a loud sounding pilot signal when there is no operator on duty or when an operator isnot wearing head receiver 20. By changing switch 16 from. contact 17 to contact 39, the pulsating direct current flows through loud-speaking receiver or howler 4-.0 instead of primary 18, thereby producing a loud audible signal capable of being heard at some distance. Relays 4:1 i2 correspond at another operatofis position to the described relays 715 and are similarly connected and operated. If it is desired that when an operator is busy the audible line pilot signal shall be sounded in the receiver at another operators position then relay 15 is provided with a contact 4:3 which is connected, as shown by the dotted line to contact 4% of relay 41-2. Therefore, relay 4:2 is intermittently energized and the audible signal consequently produced at the other operators position whenever pilot re- 41 is energized or whenever pilot relay 7 and audible signal relay 15 are men gized. Lamp 45, corresponding to lamp 8 is shown connected to contact 46 of line relay 4:7 of substation 2 corresponding to line relay 5 of substation 1 exemplifying how the line signals of difi'erent lines may be apportioned to different operators. It will be understood that if only one operator is used contact 46 would be connected to pilot relay 7.

Having obtained the number of the desired line from the calling party, calling plug 48flis inserted in jack a9 (which may be considered a multiple jack in a multiple switchboard. system or as an answering jack such as 22 ina non-multiple system). Manual ringing may be performed in the well known manner but I prefer the use of a relay such as as illustrated. which constitutes a feature of the present invention. As soon as plug iS is inserted in the jack, a path is given for ringing current from generator 50 through elements 51.

5s, 54., 55, 5e. 57, 5s. 59, e0, e1, e2. 31.. and

to ground. Call hell or annunciator 58 is continuously operated by this current. As the return path to ground is through repeating coil winding 3]. the calling party receives an audible signal in his receiver assuring him the called substation is being rung. By leaving listening key 27 manipulated until after the connection is estab lished, the operator will also receive this signal in receiver 20, which would be an assurance that the called line and the link connector were in proper operating condition and that the call bell had been rung. If

periodic ringing is desired an interrupter is inserted between 50 and 51 in a manner well known in, the art. L'hI10'tl16l"p2ttl1 in multiple relation to the ringing one is given for direct current from battery 63 through elements 6%, 65, 66, 6?. As interrupters 51-.64: alternately connect. their respective sources 5063-to contact 55, relay 6? is never traversed by the ringing current. and is not energized by the intermittent direct current until there is apath of lower resistance than that offered by elements 58 59 at substation 2. This path is given when the receiver is removed from its switchhook and relay 67 is then energ'zed. This gives a path for current from battery 6 through elements 68, right winding of relay 35, 69, 70, 71, 72, 73,, and to ground, energizing ringing relay 85. The disengagement or" contacts disconnect-s the ringing current from the substation line. Contact 66 is first connected to contact 38, and then disconnected from contact 65, thereby substituting continuous direct current from bat tcry 6 through repeating coil winding 30 for the intermittent, current from battery 63 through interrupter 6st. Supervisory relay 67 is thereby maintained actuated as long as a path for direct current remains closed at substation 2. Contact 53 engages contact 74, thereby bridging non-inductive resistance 54 around relay 67. Contact 33 is disengaged from contact 34:, thereby pre venting the subsequent manipulation of listening key 27 from connecting the operators set to the repeating coil. Therefore, it will be seen that it is impossible for an operator to listen in on a conversation passing between. two connected substations.

Vi hen the receiver is replaced on its switch-hook at substation 2 and relay 67 consequently die-energized, the disengagement of contacts 69-70 does not deenergize relay 35, as it it did the call bell at substation 2 would be rung again. Relay 35 remains energized owing to a path for direct current from. battery 6 which was closed through the left winding of said relay when the relay was first energized. Therefore, this winding constitutes a locking winding. This path may be traced through contacts 7677,

supervisory lamp, 78 and elements 71, 72,

and ground As this locking winding.

terms a shunt tor resistance 68 it is also energized by thecurrent flowing through the right winding when relay 6'7 is actuated.

Supervisoryrelay 79, which *as energized when the connection was made to the calling line,shunts supervisory lamp 80 with resistance 81, thereby virtually extinguish ing the same. This is well known in the art and the only change I have made in the function of this relay is one which may or may not be used, namely, the provision of contact 82 shOWn connected by a dotted line to contact 83 of relay These two contacts are used only when it is desired that when the calling party abandons a call previous to the response of the called party, the

ringing on the called line should cease. The

replacing of the receiver on its switch-hook at substation 1 de-energizes supervisory relay 7 9. This gives a path for current from battery 6 through the lett winding ot relay 35, elements 76-83,- 82, 8st, 85, 86, and to ground, energizing relay 35. Contact 77 engages contact 76 before the latter is dis, engaged from contact 83, thereby establishing the path already traced through superrisory lamp 78 and maintaining relay 3.. actuated during the time plug4i8 is connect ed to the called line.-

During the time the called line is being rung, a path given for current from battery 6 through resistance 68, lamp 78 and elements 71., "2, T3 and ground. This energizes cut-oft relay 73 but only partially energizes lamp 78. Therefore, the partial illumination of lamp 78 indicates to the operator that the called party has not responded, and key 2'? may be manipulated at anvv time so that the operator may listen in and note by the ringing signal in receiver 20 if the called substation bell is being rung. Nhen the called party responds and relay is energized resistance 68 is shunted by thelett winding of said relay, the resistance in series with lamp 78 being so lowered thereby that it would be fully illuminated, were it not that lamp 7 8 is also shunted at the same time by the right winding of relay 35, which is such thatlamp 78 is virtually extinguished. Therefore, supervisory lamp 78 is only fully illuminated when supervisory! relay 67 is tie-energized when the called party replaces the receiver on its switchhoolr. I v

Interrupter 6-1 is shown connected to battery 63 of lower voltage than battery 6 which is connected to the repeating coil, a condenser 87 being shown connecting a brush of said interrupter-to the wire lead ing from the brush 0t ringing interrupter 51. This use of battery 63 and condenser 8'? is what differentiates the ringing interrupter from the form shown and described in my aforementioned Patent No 1,128,262, to which reference is made for a more complete description ot the ringing system than is givenherein, it being understood that the form shown in said patent may be substituted for the form shown herein. The use of a battery of lower voltage than the regular exchange battery will be found to pre rent a possible slight energization of relay 67 by the intermittent direct current when the circuit is closed through "all-bell 5S and condenser 59 at substation 2-. The use of condenser 87 furnishes a path to ground through battery 63 in multiple relation to relay 67, whenever the latter is connected to battery 63; consequently any static charge of the called line finds a path to ground through the condenser instead of through the inductive winding oi relay 07. This static charge may be due to the discharge from the line and condenser 59, due to their charge by the alternating current. As supervisory relay 07 is not shunted by non-inductive resistance 54- until after the relay has been first energized, it can be readily caused. to attract its armature by a battery of less voltage than that necessary to cause the same attraction after said resistance bridged around its winding.

Referring now to Figure 2. the vertical line of relays and associate equi nnent, diagrammatically shown in the center of the page and below the link connector circuit, represents the apparatus individualto the position at which the link connector is located. The vertical rows at the left and right represent similar apparatus individual to the left and right immediately adjacent positions. At the left and right 0t these rows are shown parts only 01' similar apparatus individual to the next positions in line.

Line lamp or signal 89 is intended to be connected at its free terminal to-con'tact 9 of line relay 5. Therefore, when the latter is energized a path is given for current from battery 90 through pilot relay 91, left outermost armature switch and alternate contact of relay 103, line lamp 89 and to ground through contacts 9-10 of relay 5, as shown in Figure 1. Lamp 89 and pilot relay 91 are energized. giving another path for current from battery 90 through interrupter 941:, elements 95, 96, 97, 98, 99. 100 and to ground, energizing relay 99. lnterrupterQlisshunted by a resistance 101. so thatwhen. the brush of the interrupter is engaged with one of the insulating segments current still flows over the path just traced, though it will be less than when the brush engages anretallic segment. Owing to the variable current thus allowed to flow through primary 100. an al ternating current is induced in secondary 102 which is connected in a circuit including the alternate contact and right innermost armature switch of relay 103, contact 104.- of the operators set jack, contact 105 of the operators set plug, operators receiver 106, contact 107 of? the plug and spring contact 10S '01: the jack. Therefore, an audible sig nal is produced in receiver 100. Hearingorator 137.

this signal. and observing displayed line signal 89, the operator inserts answering plug 109 in the proper jack. l -Findings 110-111 ot' the repeating coil are thereby connected to the calling substation in the well known manner and when the well known form of lrtening key 112 is manipulated, a path is gii'en for current from battery 113 through elements 1141, 115, 116, 117, upper spring ct key 112, 118, 119, 121, 122, 123, 108, 107, 106, 105, 10 1, 12%, 125, 12", lower spring of key 112, 127 and to ground, energizing relay 122. This gives path for current from battery 90 through wire 128 and elements 129, 130, left winding of relay 131, right windings of relays 132 and 133, 99, 100 and to ground, on ergizing relays 131, 132, 133 and shunting the connection through relay 99 to battery 90 by way of interrupter 9 1, by a direct connection to the same battery. The energizetion of relay causes contact 97 to disencontact 93, thereby cutting off the variable current from primary 100 and. consequently eliminating the audible pilot signal in receiver 106. The constant current still flowing in primary 100 through relays 131, 132 and 133, does not produce any noticeable eltect on receiver 106, thereby allowing conversation to take place between the calling substation and the operator, inasmuch as receiver 106 is now connected to windings 116127 of the repeating coil. Relay 122 is shunted by condenser 13% so as to allow the passage of voice currents. To evade disagreeable click in receiver 106 caused by an appreciable amount of direct current passing therethrough, relay 122 is preferably of high resistance.

Having obtained the number of the called for line, the operator, if the line tests idle, inserts calling plug 135 in a jack of the line and manipulates ringing key 136 which impresses on the line ringing current from gen- The restored to normal condition of listening key 112 before ringing key 130 was manipulated, opens the described circuit through relay 122 and consequently the described circuit through relays 131, 132,

and 99 is also opened, restoring; the operators audible signal circuits to their nor mal condition. he insertion oi": plug 135 in the jack gives path "for direct current from battery 113 through callin supervisory lamp 138. resistance 139, contact 110, and the cutoii relay of the called line to ground. A shunt path for the current from battery 113 to resistance 139 is given through elements 114-, 115, 7 5, 1411, 1 12, 1 13 and 14a, resistance '15 being such that lamp 138 is only partially illuminated. This partial illumination of the supervisory lamp furnishes the signal indicating that the called party has not responded.

When the called party removes the substation receiver from its switchhook, supervisory relay 115 energized and the dcscribedshunt path from resistance 139 is opened and another shunt path is given from battery 113 through elements 111-, 116, 1 .7, lower winding of relay 118, 149 and 1-1 1, energizing relay 14:8. As the lower winding of relay 1&8 is of lower resistance than resistance 75 lamp 138 is virtually extinguished v and this condition indicates 'to they operator that the called party has responded.

;Supervisory lamp 1.50 connected to resistance 151. and energized in the same manner as lamp 138 was not illuminated when answering plug 109 was connected to the calling line, as the energization of supervisory relay 152 closed a shunt around the lamp from said. resistance through elements 153, 151, 155, 1. 17, 1&6 and 11 1.- Therefore, lamps 150-138 remain extinguished while the lines are being used.

lVhen calling plug 135 was connected to the called line a path was also given for direct current from battery 113 through wires ll.-fl-1l5, upper windings of relays 1591%8, key 176, contact 1&0 and to ground through the cut-off relay. Relays 159-148 are not energized by the current thus allowed to flow through them. However, said windings are such that they constitute looking windings, so that when the relays have once been energized by the current flowing through their other windings, they are m aini tained actuated as long as calling plug 135 is connected to a jack. The resistance of these windings is such that lamp 138 is not I shunted so as to impede its illumination. It

is for this reason that said windings are preferably connected to a point between resistance 139 and contact 140 of plug 135. These upper windings are not connected to contact 160 of answering plug 109, as in that event relay 159 might be prematurely energized when a connection is made to the calling line if contact 160 oi? the plug engaged the jack contact before the other two contacts did, as the lower winding of relay 159 would be momentarily energized, due to the non-energization of supervisory relay 152, and the locking winding would thereupon maintain it actuated.

lVhen the calling substation receiver replaced on its SWl'tCll-llOOlZ, supervisory re lay 152 is tie-energized and contact 153 disengages contact 15 1 and en ages contact 156. This gives path for current from battery 90 through interrupter 157,- disconnect relay 158, left intermediate alternate contact and armature switch of relay 103, lower winding of relay 159, intermediate winding of relay 14:8 and elements 156, 153, 151, 160 and to ground through the cut-off relay, energizing recall relay 159 and operators disconnect relay 158. If the called substation receiver is replaced on its switch-hook, instead of that of the calling substation, supcrvisory relay 145 is tie-energized and the path from the upper terminal of the intermediate winding of changing relay 14.8 in stead of being through contact156, would have been through elements 161, 142, 1 13, 144i, 139, 1 10 and to ground through the cutoff relay of the called line. Changing relay} 1 18 was energized by the previous energization of relay 145 and is maintained actuated by its upper locking winding. 'When both receivers are replaced the path through the intermediate winding of relay 1 18 is divided and passes through both cut-oii' relays. In any event operators disconnectrelay 158 is energized when either party replaces his receiver giving path for current from battery 90 through interrupter-157 and elements 162, 163, 164:, 165, 92, 100 and to ground. The variable current formed by interrupter 157 is of a different character from that formed by interrupter 94 and consequently the audible signal produced in receiver 106 by the variable current flowing in primary 100 is of a distinct character from that produced by the operation of a line signal. Therefore, the operator knows that there is a link connector which can be disconnected from a line. The shunts through resistance 155 or lower winding of relay 1 18 are removed. The shunt through disconnect re lay 158. does not impede the illumination of a supervisory lamp, or lamps. Therefore, the displayed supervisory lamp, or lamps, indicates the link connector 111 questlon.

If the calling party replaces the substation receiver prevlous to the response of the called party, then changing relay 148 is energized, due to the current flowing through its intermediate winding, and the consequent disconnection'of contacts 141 142 removes the shunt, including resistance 7 5, from around supervisory lamp 138. The consequent full illumination of this lamp warns the operator from further ringing on the called line as said ringing is only done when said lamp is partially illuminated. Therefore, the operator would take down the connection. Should the called party respond after the oallingparty has abandoned. the call and before the operator has taken down the connection, a visual and audible recall signal is given, in the man ner hereinafter described.

Whenever any of the described disconnect means are put into operation, variable current formed by interrupter 15? flows over the described path to contacts 160 or 1&0 oi the plugs. Therefore, when the usual busy test, which is well known in the art, is made on one of the multiple jacks of a connected line, instead of a click being produced in the testing operators receiver, a continuous audible signal will be produced during the time the test contact of the calling plug is in contact with the test thimble of the jack. Hearing this signal, the testing operator knows that the tested line is really idle and is calling for a disconnect and as the connecting operator must receive the same signal it can be but a moment or two before the established connection will be taken down. Therefore, instead of reporting the tested line busy the testing operator may wait a moment. or so and when the connecting operator has taken down the connection the cessation of the sustained audible signal will indicate to the testing operator that she may insert the calling plug in the jack. In this way it will be seen that a formerly busy line will really test idle as soon as the receiver'is replaced instead of when the connection is taken down. Disconnect relay 158 is maintained actuated by the variable current flowing through it.

Should the calling or called party desire a recall, instead of a disconnect, then the switch-hook is depressed once instead of several times, and is then allowed to return to its former position. The depression of the switch-hook operates the disconnect circuit, as described, and as relay 159 is energized thereby and is maintained actuated by its upper locking winding the return of the switch-hook to its former position and the consequent re-energization of supervisory relay 152 or 145, as the case may he, gives path for current from battery through elements 166, 167, 168, left innermost alternate contact and armature switch of relay 103, 169, 147; and 155, 154, 153, 151, 160 and to ground through the cut-o6? relay of the calling line; or lower winding of relay 148, elements 149, 144, 139, 140 and to ground through the cut-off relay of the called line, in either case energizing operators recallrelay 168. This gives path for current from battery 90 through interrupter 170 and elements 171, 172, 17 3, 174, 130, left winding of relay 131 right windings of relays 132133, 99, 100 and to ground, energizing the traversed relays. It will be clear that if a receiver is replaced and then removed, before the connection is taken down, or if one receiver is replaced and the other not replaced, the recall signal will also be given, The variable current formed by interrupter 170 is of a diiferent character from that formed by interrupter-s 94 or157 and consequently the audible signal produced in receiver 106 by the variable current flowing in primary 100 is of a distinct character from that produced by the operation of a line signal or by an idle link connector being connected to a line. Therefore, the operator knows that there is a line which is making a recall. The shunt which extinguishes supervisory lamp 150 or 188', was removed when contacts 146-147 of relay 159 were disengaged. However, the illumination of lamp 150 or 1538 varies as the current flowing through resistance 151 or 139 has two paths oiilered to it, one through the lamp to battery 113 and the other through resistance 155 or lower winding of relay 148, relay 16S and resistance 166 to battery 90. Resistance 166 is intermittently short-circuited by inter rupter 175, the consequent decrease in the resistance of the circuit causing the illumination of lamp 150 or 138 to vary. Interruptcr 175 revolves comparatively slowly, so that the variations in the illumination of the lamp are very noticeable. Interrupter 175 and resistance 166, as well as the other interrupters, may be connected to battery 113, if preferred, instead of to battery 90, the principal purpose in showing two batteries being one of convenience in the drawing. Relay 168 is maintained actuated by this variable current flowing through it. i

The operator on hearing the recall audible signal can select the line making the recall by observing the described variations in the illumination of the supervisory lamp of the link connector connected to that line. soon as listening key 112 is manipulated, thereby connecting the operators set to the calling or called line, or both, as the case may be, connecting relay 122 is energized, as hereinbefore described. Therefore, the path :tor the recall signal current is opened when contact 130 of relay 122 disengages contact 174. If the calling line is making the recall, and a connection to another line is desired, the withdrawal of calling plug 135 "from the jack opens the path through relays 159-148, thereby restoring them to their normal condition and de-energizing recall relay 168. It the recall is for the same line, then key 176 is manipulated, obtaining the same results. The use of key 176 is optional, inasmuch as plug 135 can always be removed from the jack to de-energize relays 159-148. If the recall is from the called line, in any event the calling plug 135 must be disconnected from the ack and an answering plug inserted, so as to be able to ring the line called for. This would also tie-energize relays 159-148.

A busy test made on a jack of a line cstablishing a recall would produce a busy signal characteristic to interrupter 175, in the same way as the described disconnect busy test was produced, thereby indicating to the testing operator that the line was establishing a recall.

Vhcn one connected line signals a recall and the other a disconnect, the respective supervisory lamps indicate this condition and at the same time the disconnect audible signal is prevented from being produced in receiver 106, as it is more important for the operator to attend to the recall first. This result isobtained by having the path of the recall variable current to primary 100 travas U erse relay ()9, energizing the latter. The consequent disei'igagement of contacts 164- 165 o't'this relay opens the path for the disconnect ariable current to primary 100.

lVhen an operator is engaged in completing a connection and a listening key 112 is manipulated, the described energization oi relay 122 as well as eliminating the audible line pilot signals also eliminates the recall and disconnect audible signals. The disengagement of contacts 13017 l of relay 122 opens the path 01 the recall variable current to primary and the energization of relay 99 and the consequent disengagement of contacts 16411'C-5 opens the path or the disconnect variable current. Therefore, an operator cannotbe disturbed by any of the audible signals while busy, but as soon as idlethe Various signals may be produced again. 1

Reference is now had to tl e audible signal and transferring relays shown in the drawing in a vertical line below the linlr connector. These relays are individual to the operators position at which the link connector is located and the connections to the same are common to all the link connectors at that position. 7

lVhenever the operator at a position is on duty thereat primary relay 103 is maintained actuated, inasmuch as a path is given for current from battery 113 through said relay as long as the two contacts of operators transmitter jack 178 are connected together through operators transmitter 179 by way of plug 180, which is inserted in said jack. As illustrated, relay 103 talres the place of the retardation coil usually used in series with the operators transmitter and primary oi. operatorsinduction coil, when the trans mitter is energized from the exchange battery. Primary 181 and transmitter 1'7 9 are usually shunted by a condenser which is not shown in the drawing for sake of clearness, the use of the same being well known in the art.

When an operator vacates a position and withdraws the transmitter plug; the circuit through the transmitter jack is opened and primary relay 103 is consequently de-energized. This condition is shown in the drawing in the vertical row at the left of the central posit-ion, wherein the reference nunierals to corresponding elements at the central position have the e: :ponenta added to them.

.The de-energization of relay 103- givcs a path for current from battery 113 through the right outermost armature switch and normal contact of said relay, left winding of relay 131 right windingsof relays 13 1323, relay 99 and primary 100. The purpose of this circuit is merely to maintain relays 131, 132 and 138 actuated, so that the transferring functions W tornied by their contacts may be attained in the same way as when said relays are energized from time to time, when the operator is on duty. As said relays may be 01 high resistance, but little current is consumed when the position is vacant.

The right innermost. and intermediate armature switches and contacts of relay 103 are merely for the purpose of changing the listening key leads of a Vacant position to the corresponding leads of the next position to the left or right, as the case may be. This allows the operator at the latter position to connect the operators set thereat to the link connectors 01 the vacant position, so that they may be used by the operator for establishing connections. If this feature is not desired these armature switches and contacts are dispensed with, and an alternative form 0'! connecting the special audible signal secondary to the operators receiver is used as shown at the next position to the left where the corresponding reference numerals to instrumentalities shown in the central position, bear the exponent b. In this form the upper terminal of secondary 102 eonnects to an extra spring 182 of the operators receiver, jack so that said secondary is eonnected direct to contact instead 01": to the same contact by way of the right innermost armature switch of relay 103 and contact 10a, as shown at the central position.

The listening key leads of the a position, corresponding to 119-125 of the, central position, are shown in a corresponding position at 183. The already described circuit from these leads which is closed through relay 122 and contacts 104"'108'- of the operators receiver jack, when the receiver plug is engaged therewith, is opened by the withdrawal of said plug when the position is vacated. As the right innermost and in termediate armature switches 01"- relay 103 are connected to the same leads 183 and as said switches-are engaged with their normal contacts which are connected to the correspondinglistening key leads 18-1 of the 6 position, it will be seen that receiver 106 may be connected to any link connector of the a position as well as those of the b position. It will also be seen that when the central position is vacated and primary relay 103 de-energized listening key leads 119- will be similarly connected to said leads 183, so that the operator at the 5 position could then use any of the link connectors at both. the a and central positions as well as those of the Z) position.

The upper terminal of audible signal secondary 102 is preferably connected to the alternate contact of the right innermost armature switch of relay 108, as if it were connected permanently to contact 104 01 the receiver jack, leads 119125 would be permanently bridged by a circuit including relay 122 and condenser 134; in multiple, secondary 123 and special secondary 102 lVhile'the resistance of this circuit may be high, yet, when several. adjoining positions were vacant the multipled resistances oithe circuits thus bridged across the listening key leads or the various vacant positions, might impede somewhat the passage of talking currents to and from the link connectors of. some of said vacant positions.

The three left, armature switches of relay 103 are connected respectively, to the line lamps of the position as shown at 89, and to the disconnect and recall circuits of the link connectorsat the position. The respective lei't normal contacts of relay 103 are connected to the corresponding armature switches of relay 103". Therefore, when the central position is vacated the illumination of a line lamp thereat, or a recall or dlsconnect signal at that position, will produce their characteristic audible signals in the operators receiver at the a position and ii"? the a position is vacant, they will be produced in the receiver at the Z) position or if that position is vacant at the next position to the left at which there is an operator on duty.

It will be readily understood that the direction of the transfers performed by relay 103 is purely arbitrary and that the same may be to the right if desired, or some positions may transfer to the right and others to the left. lily idea is providing for these transfers is to provide means whereby an operator who is in charge of several vacant positions maybe positively and instantly advised of an initiated call, a recall. or a disconnect at any of the vacant positions.

-Considering now that all the positions shown are occupied, then when pilot relay 91 is energized by a line initiating a call and at the same time the operator receives recall or is engaged in completing a connec tion. left transfer relay133 is energized, as has been described, and the path for the variable current through contact 9'7 is transferred from contact 98 to contact 185 and thence through the left winding of relay 133 to the a position. It the operator thereat is idle: that is has no recall to attend to or is r not busy coin 'ileting a connection. then the path proceeds by way of contacts 186137 of relay 131 right windings of relays 132-133, relay 99 primary 100, and to ground, energizing all the traversed relays. The variable current thus allowed to flow through primary 100 produces the audible line pilot signal in the receiver of the operetor, whereupon this operator would attend to the call. The energization of relay 133 would in turn transfer to the Z) position any pilot signal produced by the energization of pilot relay 91", inasmuch as they are connected in the same way as are relays 91133 relays 133 able current through contact 186 is re-transierred from contact 187 to contact 188 and thence through the right winding of relay 131" to the position at the right of the central one, where the instrumentalities corresponding to those oi: the central position are denoted by the use of the exponent c. If the operator thereat is not receiving a recall,

is not busy establishing a connection or is not receiving a transferred signal from the next position at the right by Way of relay 131 then the path proceeds by way of contacts 189 -190 oi" relay .132 right winding of relay 133. relay 99, primary 100 and to ground, energizing 99. Therefore, the operator at the 0 position would attend. to the call. On the other hand it the operator at the c position is receiving a recall, or is busy establishing a connection, or is receiving a transferredsignal, then relay 132 would he energized and contact 189 would disengage contact 190 and engage contact 193. This would re-transfer again the path for the variable current and it would proceed by Way of the left winding of relay 132 to contact 19% otoperators recall relay 168. If the central position is receiving a recall, then the path is open at this point, as contact 173 would be engaged with contact 172. If the operator at the central position is connecting, then connecting relay 122 is energized and the path is open at contact 17 1. Therefore, the variable current controlled. by pilot relay 91 has no path to ground, and no audible pilotsignal is sinuided as long as the central or originating position and the left and right adjacentpositions are all occupied. However, such a path is furnished and the signal produced at the first one of the tiree positions to become idle. If the central position becomes idle first, due to the release of the recall signal. or the completion of the connection, contacts 173 or 130 of relay 168 or 122, disengages contact 1'72 or 129, as the case may be, and before the circuit can be closed again (at-"contacts 19% or 179;, relay 133 is de-energized and contact 97 of relay 133 disengages contact 185, thereby opening the described path to contact 19% of relay 168. Consequently relay 133 remains tie-energized and when contact 97 engages contact 98 the audible pilot sis ial, is produced in receiver 106. If the a position becomes idle first, as

no m

soon as contact 186 of relay 131 'engages contact 187 the path to ground is closed through primary 100 and the signal consequently produced in the operators receiver thcreat. As this path includes the left or looking winding of relay 133, this relay will remain enerqized should the operator at the central position now become idle. Thereiore,the signal not cut off from. the a position and sounded at the central position, as it would he were it not for this locking winding. If the operator at the a position answers the. call, the consequent energization of'connecting relay 122 energizes relay 131 and as soon as contact 186 discngrges contact, 187., the circuit through thi locking windingis opened and relay becomes tie-energized. If the 0 position becomes idle first, as soon as contact 189 of relay 132 engages contact 190, the path to ground is closed through primary 100 and the signal produced in the operators receiver thercat. this path includes the right or looking winding of relay 131 as well as, the locking winding of relay 133, both of said relays remain energized should the operators at the central and (1. positions now become idle. Belays133 and 131 are de-ener ized when relay 122 is energized. Therefore, it will be seen that once a transferred or ire ti'ansferred pilot signal has begun tosound in an operators receiver it cannot be cut-off and sounded in the receiver of another operator if the latter subsequently becomes idle, This is so arranged. to evade the resultant confusion of having one, two or three operators receive one after the other the same pilot signal produced by the same illuminated line lamp, as it is one of the purposes of these audible signals to provide means whereby only one operator can ever attempt to connect to a calling line at the same time. However, these locking windings maybe eliminated if this feature is not desired.

When.- the operator at the central position is idle and a signal is transferred thereto fromthe 0 position or re-transferred thereto fromthe 6 position, relay 133isenergized in either case, and the signal controlled by pilot relay 91 will. be transferred and r e-trans ferred in the same way as hereinbefore described, excepting;- that recall relay 168 or connecting; relay 122 will not be energized. Therefore, if the a operator is busy and the 0 operator either busy or receiving a transferred signal, a path is given for theyari able current at contact 194: of recall relay 168 and the same proceeds to primary 100 through contacts 178 and the same path as traced for the recall audible signal. This would energize both relays 131 and 12:12. so that they would perform their transferring and re-transferring functions. Therefore, it will readily be observed that a have transferred or re-transferred pilot signal only takes precedence over the pilot signals originating at a position, when there is an adjacent operator able to attend to the latter. As this path for the signal current controlled by pilot relay 91 wouldlbe through the locking windings of relays 133, 131" and 132, once the variable current has begun to flow over the described pat-h, these relays cannot be (lo-energised and the path cannot be interupted by the operators at the a or 0 positions subsequently becom le. l-lowever, when the central operator attends to the call v the energization of connecting relay 12:21. opens the path at contact 17%, so that relays 13.1, 132 or both may then be (lo-energized.

lit will readily be seen and understoodthat the various transferring and re-transferring functions performed by relays 131, 132 and 133, might be performed by one relay, by makingthesamecontrol all the contac trolled by the aforesaid three rela xs. .evcr, werethis done, it would be possible to have two or three pilot signals sounding at thesame time-in the one-receiver and were these signals of different character (as heretransfers and re ransfers all the pilot signals; third, the transfer to a position of a pilot, signal from the left or right adjacent position, as the case may he, stops the production of the disconnect signal. re-transl'ers to the originating position a pilot signal retransferred from the left or right adjacent position, as the case may be, of said originat inp; position, and transfers the pilot signals of the position itself; fourth, the; re-traiisfer to a position of a pilot signal from the left or right adjacent position, as the case ma v be, of the originating posit-ion, stops the production of the disconnect signal and transfers the pilot signals of the position itself; fifth, theproduction of apilot signalat a position stops the production of the disconnect signal; sirrtluthe production of the disconnect signal. Therefore, only one signal is sounded at a time and the sounding of a signal which takes precedence over the others, automatically and instantaneously transfers the others to other operators positions or stops their production. In this wav simultaneous calls at different positions have an opportunity of being attendcdto by dif- 1 ,aeaevs ferent operators. Also the relays are greatly simplified by using them as shown, there being but one moving member for each relay and but one or two contacts engaged by said member. Relay 99 is the his relay traversed by any of the var'able currents before primary 100 is traversed, therefore, it is always energized when any pilot si nal is produced in receiver 106. As the diseng e ment of contacts 164lo'5 of this relay opens the path for the disconnect variable current, the disconnect signal is always prevented from being sounded until after the pilot signal has been attended to.

Lamps may be connected to the relay contacts as shown at the a position, if visual pilot signals are desired. Resistance 92 connected to contact 165 of: disconnect cut-cit relay 99 is used so as to prevent alow resistance shunt being formed around the various transfer and re-transier relays which at one time or another are energized. This shuntwould be formed when disconnect relay 158 connected primary 100 to battery by way of interrupter 157 and its resistance shunt.

he an operator at each posit-ion may receive an audible pilot signal denoting a call from a line assigned to that particular position, or a pilot signal from the position at the left or right, it is advisable to provide means whereby the character of signal sounded indicates the position which is to be searched for a displayed line lamp. To accomplish this result three interrupters, 191, 192, 9 1, are employed, each interrupter being so arranged that the variable current formed by the same is of a different character from that formed by the other two. Consequently, the audible signals produced by these variable currents differ from one another. Therefore, if the contacts of the pilot relays 91 of three adjacent positions are connected respectively to a diiierent interrupter, in whatever way the audible ials are transferred an operator will .lrnow from the character of the signal from what position it emanates. As illustrated in the drawing, contact 95 (not shown) of the a position would be connected to interrupter 191, the corresponding contact 95 is shown connected to interrupter 192 and contact 95 of the central position connected to interrupter 94. The corresponding contact of the 0 position would begin to repeat the sequence, being connected to interrupter 191. The variations in the variable current formjug means of these interrupters are purely arbitrary and I have chosen the form shown for purposes or illustration on account of it furnishing simple signals which can readily Interbe distinguished from each other. rupters 191.; 192 and 9 1 are intended to re vclve comparatively slowly. As long as their brushes are engaged with the insulating segments of the interrupter-s, the path from battery 90 is through the resistances, such as 101, which shunt said interrupters. Suflicient current can traverse these resistances to maintain actuated whatever transferring relays may be connected in circuit with the interrupters. However, when the brushes engage the metallic segments of the interrupters the resistance shunts are shortcircuited and consequently the resistance of the circuit or circuits connected to the interrupters is lowered. This produces a click in the operators receiver or receivers, due to the variation in current strength in. primary 100. interrupter 191 has one metallic segment; therefore, but one click is produced in said receiver. interrupter 192 has two metallic segments separated by a short insulating segment and then a longer insulating segment; therefore, the audible signal formed by this interrupter is two clicks an interval then two clicks, and so on. Interrupter is similarly arranged so as to form three clicks and an interval. It the respective adacent operators positions are numbered 1-23, repeating the sequence for all the positions at the switchboard, and the pilot relay contact connected to the corresponding signal forming interrupter, it will be clear that an operator cannot mistake the originating position of any audible pilot signal. The speed of rotation o'l these interrupters should be such that the number of clicks can readily be determined. By adding other forms 01 interrupters as many positions as desired can be given indiridual character designations.

Referring now to Figure 3, as the link connector and audible signal system illustrated represents modifications of that shown in Figure 2 only that part of each which difi ers from what has been already described will be described hereinafter, it being umlerstood that those parts not described function in the same way as corre sponding parts in .ligure 2. i

The principal. change made in the link connector illustrated is that no listening or ringing keys are used. The energization of a. line lamp or signal 201 energizes pilot relay 202. This gives path for current from battery 203 througl'i elements 204, 205, 206. 207, 208, 209. 210. 211 and to ground. A. path for alternating current is given over the same path formed by secondary 205 due to the interrupted current flowing in primary 212. Primary212 and secondary 205 may constitute windings of an induction or re peating coil. Primary 212 may be of a high resistance while secondary 205 may be of a low resistance, thereby obtaining economy in the use of current from battery 203 and impeding but little the passage of current from the same battery through said second ary. interrupter 2 3 intermittently gives path for current from battery 203 through primary 212. Therefore, the alternating current produced in secondary 205 will be in accordance with the metallic segments of said interrupter. Tnterrupters 214 and 215 function similarly to 213, the three interrupters furnishing the audible pilot signals current for three adjacent postions at the switchboard, as described in relation to interrupters 191, 192 and 94: in Figure 1. The interrupters are the same, the connections only being different, 'Operators receiver 216 is in circuit with secondary 217 and windings 218219 of an operators repeatin coil. Therefore, the alternating current traversing primary 211, induces a corresponding current in secondary 217 which produces the audible signal in receiver 216.

When answering plug 220 is inserted in the answering jack of the calling line, tip and ring contacts 221222 are not connected to battery through supervisory relay 223 and the link connector repeating coil windings 2241225, but instead are connected to battery through said relay and the operators repeating coil; the path being as follows: battery 203, elements 226, 227. 228, 229 and engaged armature switch, 230, 231, 232, 223: and 233, 23 1, in multiple relation to 223; 222 and thence to the substation line, returning through 221, 236, 237, 238, armature switch and engaged contact 239, 240, 241 and to ground, energizing supervisory relay 223 and connecting relay 241. This gives path for current from battery 203 through elements 226, 227, 212, 2-13, 24.4., 24:5, 24:6, 247, 2&8, 2 19, 250, 251, 211. and to ground, energizing all the traversed relays. The energization of relay 251 causes contacts 209-210 to be disengaged, thereby preventing the production of the audible pilot signal, controlled by pilot relay 202. Conversation can 110w take place between the calling party and the operator, due to the connection of the latters receiver to the operators repeating coil windings. Relay 2 11 is shunted by a condenser to facilitate the passage 01? the voice currents; The operators transmitter is shown connected to primary 252 associated with the same secondary as audible signal primary 211. It preferred, separate induction coils may be used, as shown in Figure 2. The dotted lines connecting the operators transmitter, represent the transmitter jack connections as shown in Figure 2.

When calling plug 253 is inserted in the jack of the called line a path is given for ringing current from generator 254 through elements 255, 256, 257, 258, 259, 260, 261, called. substation call-bell, 262, 263, 264, 238, armature switch and engaged contact 239, 240, 2 11, and to ground. As the ringing current has returned to ground through winding 240 of the operators repeating coil, both the operator and the calling party receive an audible ringing signal in their respective receivers.

The insertion of the calling plug also gives path for current from battery 265 through elements 266, 267, 268, 269, 270, 271, lower winding of 272, 273, and to ground through the cut-off relay, energizing the latter and relay 272. Relay 272 may be made slow acting, due to its upper short-circuited winding as shown, or by any other means, provided it is desired that the operator should receive the ringing signal when a connection is made to a called line, thus assuring the operator that the called line is in working condition and that the call-bell has been rung. When relay 272 is energized contacts 27 1275 first engage contacts 232236, thereby connecting repeating coil windings 224-225 to the calling line, and then disengage contacts 232* from contacts 231--237. In this manner supervisory relay 223 is not momentarily de-energiz'ed though it and the calling substation now receive current from battery 265. The operators repeating coil and consequently the operators telephone set, is disconnected from the link connector when contacts 231-237 are disengaged and the described circuit through relay 2&1 is opened and consequently the described circuit through relays 245, 246, 2 17, 24:8, 2 19, 250 and 251 is also opened, restoring the operators audible signal circuits to their imrmal condition. The engagement of contact 276 of relay 272 with contact 263 and the disengagement of the latter from contact 26 1 changes the ground connection for the ringing current to winding 277 of the cord repeating coil; consequently, the calling party only continues to receive the ringing signals. The engagement of contact 278 with contact 279 and the disengagement of the latter from contact 280, prevents the connection of the called line to the operators repeating coil, when the called party responds, and instead connects it to winding 281 of the cord repeating coil.

The automatic ringing system illustrated in Figure 3 is a modified form of the system illustrated in Figure 1 and described in relation thereto. Interrupter 282 is used instead of condenser 87 (Figure 1) for the purpose of relieving the calledline of static charges, thereby similarly avoiding the necessity of adjusting the supervisory relay so that it will not be actuated by the charge retained in the called substation condenser and line due to the impressions of ringing current. lnterrupters 283 and battery 28 1 correspond in function to interrupters 51-6 1 and battery 63 shown in Figure 1 and de scribed in relation thereto. Interrupter 283 is connected by way 01 elements 285. 286

and 287 to plug contact 261. Interrupters as illustrated revolve in a adirection and are so mounted that their speed of rotation and the relative position or" their metallic segments is always the same. Therefore. when the brush of interrupter has disengaged ametallic segment and is engaged with one of the insulating segments, the brush 0t interrupter 282 engages a metallic segment. thereby closing the cirruit through the called line directly to grouml and consequently the charge retained in the line and substation condenser is led directly to ground instead of to ground by way of supe ""sory relay 287, interrupter 283 and battery 28%. When the brush of interrupter 282 has disengaged the metallic segment and is engaged with one of the insulating segments, the brush of interrupter engages a metallic segment, thereby connecting battery 284i to the called line through supervisory relay 287. When the brush of interrupter 283 has disengaged the metallic segment and is engaged with one of the insulating segments, the brush of interrupter 255 engages another metallic segment and the sequence of operations is re peated. In this way, the called line is momentarily short-circuited after each impression of ringing current and consequently no line discharge can ever take place through supervisory relay 287. Interrupters 255, 282 and 283 are illustrated diagrammatically only and their respective metallic segments are shown being equal in size. However, this is not essential and the metallic segments of interrupter 282 may be smaller than the corresponding segments of the other interrupter-s, inasmuch as th static discharge is practically instantaneous. By making the metallic segments oi interrupter 282 smaller, those of interrupter 283 may be made correspondingly larger, thereby allowing longer impressions of the intermittent direct current for operating supervisory relay 287 when the called party responds.

thipervisoiy lamp 288 is only partially illuminated due to the shunt path to battery 205 from resistance 289 through elements 290. 291. 292. 294 295. Interrupter preferably revolves at high speed so that shunt is suliiciently maintained to obtain the desired partial illumination oi? lamp 288, yet the same time its insulating segments are such that if a. busy test is made on a multiple jack of the same line to which plug is connected the variations in current strength at the tested jaclr will produce a sustained audible busy test in the testing operators receiver which will be distinctive to interrupter 295.

Supervlc lamp 296 is not illuminated.

the

due to the shunt path from resistance 297 y throi elements 298., 209. 300. 301. 302. 303 interrupter 303 is similar to 295.

though it has a different number of insulat ing segments. Therefore, a busy test made on a multiple jack of: the calling line will give an audible busy test signal distinctive to interrupter 303, interrupters 295-303 may be shunted by a resistance such as 305, though the use of such a resistance is not essential. its two busy tests are provided, one peculiar to the talking condition of a line and one peculiar to the ringing condition of the line. a testing operator is enabled to report to a calling party which condition it is that makes the line busy.

When the called party removes the substation receiver from its switch-hook, supervisory relay 28. is energized and the described shunt path around lamp 288 through resistance 289 is opened and another shunt path. is given therethrough from battery through interrupter 303, elements 302. 301, upper winding of ringing relay 306, 307, and 290. energizing relay 306. t interrupter 303 is not shunted by a resistance the current flowing over this path is an intermittent one: however, ringing relay 306 is nevertheless maintained actuated, without any vibration of its armature as when contact 267 disengages contact 268 the short-circuit around the lower winding of said relay is removed and the constant current flowing through this winding is sufiicient to actuate it or maintain it actuated. As the upper winding of relay 306 is of lower resistance than resistance 294k, lamp 288 is now virtually extinguished, which indicates to the operator that the called party has responded. As the shunt around lamp 288 is now through interrupter 303 instead of 295, any further busy tests made on the called line will give the testing operator the talking busy test.

The energization of ringing relay 306 causes contact 308 to first engage contact 286 and then disengage the latter from contact 285. By this means the path for current through supervisory relay 287 is changed from interrupter 283 to battery 265 by way of winding 281 of the repeating coil, thereby completing the telephonic connection of the calling and called substations. Contact 257 disengages contact 256 and engages contact 309, disconnecting non-inductive resistance 260 from ringing interrupter 255 and connecting it to the other terminal of relay 287. thereby bridging said resistance around the winding of said relay and cutting off the impression of ringing current on the called line. Contact 268 disengages contact 267. thereby removing the short-circuit around the lower winding of said relay. Consequently, the current flowing through relay 272 now flows through this winding. thereby maintaining relay 306 actuated. independent of its upper winding, so that when supervisory relay 287 is de-energized ringing current is not again impressed on the called line.

station receiver, supervisory relay 223 is de energized, giving path for current from battery 203 through elements 220, 227, 310, contact 312 and engaged armature switch, 313, upper winding of relay 31%, 315, 298, 297, 310 and to ground through the cut-oil relay, energizing relays 310-31l If the called substation receiver is replaced, instead of that of the callii'ig substation, supervisory relay 287 is de-energized and the path from the upper terminal of the upper winding of relay 314 instead of being through contact is through elements 317, 292, 291, 290, 289, 273,. and to ground through the out off relay of the called line. W hen both receivers are replaced the path from said winding is divided through both cut-off relays. In any event disconnect relay 310 is energized giving path for current from battery 203 through elements 204, 318, 319, 320, 321, 322, 323, 324:, 249, 250, 251, 211 and to ground, energizing all the traversed relays. Interrupter 325, causes a current to be induced in secondary 318, which is distinct in character from that induced in secondary 205 by interrupter 213. Therefore, the audible signal sounded in receiver 216 is distinct from the audible pilot signal. Illuminated lamp 296 or 288, or both, indicate the cord to disconnect, as the shunt path through disconnect relay 310 does not impede their'illumination. Any busy tests made on a line which is signaling a disconnect, will produce the well known click only, as the disconnect relay is connected by way of wires 227--226 direct to battery 203 and not by way of an interrupter as shown in Figure 2. Therefore, When this form of busy test is used the production of the click in the testing operators receiver, would indicate to that operator that the line is really idle and is signaling a disconnect and the testing operator could then wait a moment before connecting to the tested line, the absence of the click indicating.

when the link connector has been removed by the connecting operator.

It Will be noted that the busy tests illustrated in Figure 3 and described in relation thereto, are just the reverse from those illustrated in Figure 2 and described. in relation thereto. It will be readily seen and linden stood, that this is merely an alternative form and that either form may be used with either of the illustrated link connectors or signal systems.

If the calling party replaces the receiver previous to the response of the called party. relay 31a is energized, as described, and contact 259 disengage's contact 258, thereby disconnecting non-inductive resistance 260 from ringing interrupter 255. This prevents the continued ringing of the called partys call-bell after the call has been abandoned by the calling party. As relay 306 is not energized, supervisory lamp 288 remains only partially illuminated and as lamp 296 would be fully illuminated, the operator would know that the calling party had abandoned the call. Should the called party respond after the calling party has abandoned the call and before the operator has taken down the connection then supervisory relay 287 is energized as the intermittent current formed by interrupter 283 was not disconnected from the called line when the ringing current was disconnected. This would establish a recall and the corresponding au 'li ble signal would be sounded and the visual signal displayed, as hereinafter described.

The described energization of recall relay 314: causes contact 271 to disengage contact 270, thereby removing the short-circuit around the lowering winding of said relay. r

iherelore, the current flowing though relay 272 now flows through this winding, thereby maintaining relay 3let'actuated, independent of its upper winding. Contact 233 dis engages contact 234, thereby o iiening the shunt around the winding of supervisory relay 223 through non-inductive resistance 235. The removal of this shunt facilitates the subsequent energization of relay 223 if a recall is made, inasmuch as it will now receive all the current flowing through the calling line. The disengagement of contact- 25911'010'1 contact 258, opens the shunt around the winding of supervisory relay 287 through non-inductive resistance 260; consequently the energization of relay 287 is similarly facilitated. Therefore. the reenergization of either relay 223 or 287, gives path for current from battery 203 through elements 204;, 327, 328, 329, alternate contact and right innermost armature switch of primar-y relay 330. 331.. 301; and then by way of 300. 299. 298, 297, 316, and to ground through the calling line cut-off relay; or by way of upper winding of relay 306, 307 290, 289. 273 and to ground through the called line cutoff relay, in either case energizing operators recall relay 329. This gi es path for current from battery 203 through elements 20st. 332. 333, 335, 336. 2 5 24A. 245. 246. 2427, 24s, 24s, 250, 251., an and to ground, energizing all. the traversed relays. The variable current induced. in second 332 by interrupter 337, produces the proper recall signal in receiver 216. The illumination of lamp 296 or 288 varies, as the currei-rl flowing through resistance 297 or 289 has paths offered to it, one through the labattery 265 and the other through resi, 300 or upper winding of relay 306, recal relay 329 and resistance 327 to battery 203. Resistance 327 is intermittently shortencuited by interrupter 338, the cor-sequent decrease in the resistance of the circuit causing the illumination of lamp 296 or 288, or both. to vary in accmrdauce with the speed with which interrupter we rotates. Ea;-

teries 203--265 may of course be the same battery.

The operator is enabled to listen in on the link connector only after a disconnect or recall signal is given. This assures the subscribers of secret service and guarantees their conversation against any interruptions, either accidental or deliberate. At the same time itenables the operator to listen in and talk to either or both of the connected substations, whenever operating conditions re quire it. lVhen relay 31a is energized. contact 271 engages contact 339, which is connected to. spring 19 9 of key 3 10. This allows the manipulation of key 3 10 to shortcircuit the winding of relay 272, thereby tie-energizing said relay and substituting the connection of the operators repeating coil to the calling and called lines for the connection of the link connector repeating coil. As relay 314 is not energized while a conversation is taking place between the connected substations it will be evident that the manipulation of key 310 could not possibly obtain this short-circuit. The engagement of sprin 200 with its two contacts, when key 340 is used, connects non-inductive resistance shunts 235-260 to contact 232 of relay 272. so that supervisory relays 223 287 are again shunted by the same, notwithstanding that the actuation of relay 3141- opened the connection of the shunts. This connection of the operators repeating coil causes connecting relay 241 to be energized and the path for the recall signal current is opened when contact 243 of relay 2 11 disengages contact 336. If the recall is from the calling line and it is desired that thesame called line be rung again, key 34-1 is manipulated, thereby shortcircuiting the lower windings of relays 31 1306 and consequently deenergizing the same. As soon as contact 271 of relay 314: engages contact 270 and contact 268 of relay 306 engages contact 267, the lower windings are separately short-circuited, so that key 3 11 may be restored to normal. On account of key 3&1 needing to make a momentary engagement only with its contact it may be of the self restoring type. Key 3 10 may be of the same type if the winding of relay 272 is such that it receives enough current to initially actuate the relay only when the lower winding of relay eis short circuited though once actuated it ll remain when the short-circuit is removed. The use of key 3&0 or key 3 11, or-both, is purely optional, If only recalls from the calling line are to be attended to. the withdrawal of calling plug 253 from the line jack would doenergize relays 31 27 2 and 306.

If relay 31% is made to control the connection of non-inductive resistance shunt around supervisory relay 223, as hereinbefore described. when plug 220 is connected to the calling line, relay 223 may not receive sufliclent current to operate it as it will be shunted by this resistance. 'l herefore relay 314 would be energized in the same way as if a disconnect was signaled and this energization would disengage contacts 233---J3et thereby removing the shunt. This would cause relay 223 to receive all the current flowing to the line and cause its armature to be attracted, thereby opening the disconnect circuit and die-energizing relay err which thereupon restores the shunt.

When the well known form of busy test is made, which consists in touching contact 262 of calling plug 253 to the sleeve contact (such as 72 or 86 in Figure 1) of the tested jack, if the line is busy a path is given from interrupter 303 or 295 or batteries 265203. as the case may be, through the connected link connector to contact 273, (as hereinbefore described) the sleeve contact of said jack. the corresponding tested sleeve contact in multiple relation thereto. said contact 262 and elements 263, 264;. 238, armature switch and engaged contact 230 24:0, 211, and to ground. The current flowing through the winding 240 of the operators repeating coil produces the busy test in operators receiver 216 and that of the calling substation. Therefore, as the talking and ringing busy signals are sustained ones, the calling subscriber is automatically ad vised of this condition.

Reference is now had to the audible signal and transferring relays shown in the drawing in the vertical line below the link connector. These relays are individual to the operators position at which said link connector is located and the connections to the illustrated link connector are common to all the link connectors at that position.

F our more relays are used than in the sys tem shown in l igure 2 and described in relation thereto. However the principle is the same and it will be seen that the four relays are added to further divide the transferring functions. Primary relay 330 corresponds in function to relay 103 in Figure 2. When the position is vacated and relay 330 de-energized the left outermost and three right armature switches transfer their corresponding link connector leads to the corresponding armature switches of relay 330. However, when the right intermediate. arinature switch disengages contact the latter engages contact 315?. This e path for current from battery 203 through repeating coil winding 228, said contacts and relays 245, 24.6, 247. 24s, are. 250, 251 and to ground through primary 211, energizing all the traversed relays, thereby permanently maintaining their transferring functions during the time the position is vacant. The transfer of the connection from the line nals such as 201 or 201 is different from th described in relation to relay 103 in Figure 2. The 0 position is shown vacant and. when lamp 201 is energiz il path is given through the left intermediate armature switch and normal contact of relay 330. left innermost armature switch. and alternate contact or re lay 330,pilot relay 3at3,wires 227226,batter v 203, and. to ground, energizing relay 34:3. This gives path for current from battery 203 through elements 20%, 3-H, 3l5, 3&6, 3&7, 335, 336, are, an, 2.15, are, an, are, 2 19, 250, 251, 211, and to ground, energizing all the traversed relays. The audible signal produced in receiver 216 by the closure of this path will. be different from that produced by the energization of pilot relay 202, inasmuch as the variable current is formed by interrupter 215 instead of 213; consequently, the operator knows that the pilot signal sounded originated in a position to the right. At the same time should a line lamp be illuminated at the central position, the energization of relay 251, transfers the corresponding pilot signal to the next position at the left. Therefore, the vacant position pilot signals take precedence, the energization of the other transfer and re-transfer relays, attending to the proper re-transferring of other audible signals. As well as obtaining a distinct pilot signal from a vacant position the use of pilot relay 34-3, prevents a pilot signal from a vacant position at the right of an operator from being transferred to the next position at the left of said operator, as in that case the operator at this left position would have to reach around the first mentioned operator, something which might be difficult to do. if the form shown in Figure 2 is used, wherein the line lamps of a vacant position are connected to the same pilot relay at the next position to the left as are the line lamps of that position, a pilot signal produced by a line lamp of either of the positions is transferred whenever the operator is busy or receiving other audible signals. Therefore, for the convenient working of the system, when that form is used, the positions are so vacated that whenever an operator has vacant position atthe right, she also has a vacant position at the left. With the form shown in Figure 3, this is not necessary and the positions may be vacated in any manner desired. The pilot signal from the vacant position or positions, as described, is arranged to take precedence over any audible signal at the central position, excepting a recall. This is done as the other pilot signals which, at one time or another, are sounded in the receiver the central position can be attended to by the op erator at the a position. Therefore, the pilot signal of the vacant position or positions transfers or re-transfers said signals to the a position. When the central operator is connecting and connecting relay 24:1 15; consequently energlzed, the vacant position pilot signal path is opened at contact If a recall is made, the same path is opened at contact 347 of relay 329.

The principal difference in the pilot signal transferring means shown in Figure 3 from that shown in Figure 2, is that in addition to the functions of the latter, the former allows the operation of the disconnect signal also to transfer the line pilot signal to the a position and if the operator thereat is receiving a disconnect signal this also re-transfers the pilot signal to the 0 position and if a disconnect signal is op erating there also, this also re-transfers again the pilot signal to the central position where it ellmina-tes the disconnect signal and the other transferred signals and is sounded in operators receiver 216. It is so arranged that if the central operator is busy, or is receiving a recall instead of receiving a disconnect signal, the pilot signal isagain transferred to the a position, where it eliminates the disconnect signal and is, sounded in the receiver thereat, or if the operator at that position, instead of receiving a disconnect signal, is busy or is receiving a recall or apilot signal. from that position which cannot be attended to by another operator, then it is again re-transferred to the 0 position where it is sounded in the receiver thereat or if the operator instead of receiva disconnect signal is busy or is receiving a recall or a pilot signal which takes precedence, it is either transferred to still another position or is prevented from being sounded until one of the operators becomes idle. In this way, a disconnect signal is always given precedence over any of the line pilot signals, provided there is another operator able to attend to said pilot signals. This tends to greatly facilitate the disconnections from formerly busy lines and at the same time does not delay the incoming calls.

Consider now that the three positions shown are all occupied, and that a disconnect signal is being sounded at the three positions. Relays 310, 310, 310, are energized, thereby energizing relays 251, 249 250. If pilot relay 202 is now energizec, relay 251, transfers the path for variable current to relay 249 which re-transfers it to relay 250, which re-transfers it again to relay 245, whence it proceeds through contacts 349, 35 0, and relays 2&6, 24:7, 2&8, 2459, 250, 251, primary 211, and to ground, energizing the traversed relays. Relay 24.8 opens the path for the disconnect signal current therefore the pilot signal is sounded in the place of the disconnect signal. If the central operator is connecting or receiving a recall instead of a. disconnect signal then relay 245 is energized and the variable current path is transferred to relay 246 and thence by way of contacts 351 -3523 re- 

